In industry, loose carbon black is commonly formed as carbon black pellets by a pelletization process, since carbon black in the pellet form provides an increased density and easy handling and transportation. Also, carbon black in the pellet form is easier to use in the various processing equipments. Therefore, most of the industrial applications involving carbon black demand pelletization. Conventionally, a pelletization process involves adding a solution of water and a binding agent to carbon black powder to obtain a mixture, the mixture is pelletized in a drum pelletizer or a pin pelletizer. Later, thermal processing is provided to dry the pellets obtained from the pelletizer so as to remove the moisture.
One major drawback of the conventional pelletization method is the improper distribution of water and binding agent in the mixture with carbon black. To overcome this drawback and meet the pellet quality requirements, excessive water is added. Later, during thermal processing, the water is removed by application of heat, typically in a rotary drum dryer. Excess water results in an increased load on the dryer and a resultant drop in the production output of the process. Also, the energy required for drying and the time taken in drying is increased due to the excess water. Therefore, the uniform distribution of water and the binding agent in the mixture with carbon black is crucial in the pelletization process. Further, due to improper distribution of the pelletization components, the quality of the carbon black pellets so produced is not uniform.
The use of dispersing agents has been studied in the past, so as to effect a more uniform dispersion of the carbon black in an end-use application, for example: in rubber or plastic. However, there is still felt a need to provide an improved pelletization process which ensures uniform distribution of water and the binding agent in the mixture with carbon black, so as to obtain carbon pellets having uniform quality.
Several attempts have been made to provide a pelletization process for carbon black that overcomes one or more of the drawbacks listed above. Some of the disclosures are listed in the prior art below:
U.S. Pat. No. 3,776,750 discloses a two-stage process for pelletizing carbon black. The first stage comprises forming a first mixture of carbon black and an oil-water emulsion and the second stage involves adding water to the first mixture to obtain a second mixture. The second mixture is then agitated to form carbon black pellets. The process as disclosed in U.S. Pat. No. 3,776,750 aims at providing soft pellets which can be disintegrated easily and dispersed in rubber.
U.S. Pat. No. 3,956,445 discloses an improved carbon black pelleting method which produces layered pellets having relatively high density. The method comprises the steps of combining an aqueous pelleting liquid and loose carbon black in a weight ratio of about ⅔ to 2, and agitating the resultant mixture in a pellet mill to form pellets. Additional carbon black is added in a series of increments and additional water is finally added. By controlling the relative amounts of carbon black, pelleting liquid, and the time of addition of incremental carbon black, the layered pellets are formed.
U.S. Pat. No. 4,102,967 discloses a method for pelleting carbon black to produce layered carbon black pellets having a hardened outer shell. The method comprises the steps of: introducing an aqueous pelleting liquid and loose carbon black in a weight ratio of about 2:3 to about 2:1, agitating the mixture in a pellet mill to form pellets, introducing additional carbon black into the mill, and finally introducing an additional liquid containing ammonium lignin sulfonate or hydrocarbon oil into the mill to obtain layered pellets. The layered pellets so obtained reduce dispersion related problems and dusting problems while handling.
The present disclosure aims at providing an improved process for pelletizing carbon black, the process primarily aims at providing a uniform distribution of water and the binding agent on the surface of the carbon black pellets, thereby, providing uniform dispersion of carbon black in end-use applications. Also, the present disclosure aims at reducing the water consumption and conserving energy while increasing the productivity and enhancing the pellet quality.